The present invention relates to a jack mounted to various kinds of devices such as an audio device, a video device, etc. In particular, the present invention relates to a jack with a shield plate that improves resistance to electrical noise and interference.
Referring to FIG. 9, a conventional jack 100 with a shield plate 3 and a jack body 2 is shown. Jack body 2 is mounted on a circuit board 4 and has several terminals connected to a circuit pattern on circuit board 4. The terminals are arranged within an insulating housing constructed of synthetic resin formed in a rectangular parallelepiped shape. In FIG. 9, reference numerals 5a, 6a and 7a respectively designate leg portions of a sleeve terminal, a chip terminal and a ring terminal. These leg portions extend through a rear face side of circuit board 4. Leg portion 5a is solder-connected to a ground pattern of circuit board 4, which is connected to a circuit board ground. Leg portion 6a and leg portion 7a are respectively solder-connected to unillustrated signal patterns of circuit board 4, which provides an electrical connection to a predetermined circuit.
Jack body 2 is mounted to a metallic chassis 9 of a device with a cylindrical sleeve 8. Sleeve 8 is located on an insertion side of jack body 2.
Shield plate 3 has a covering portion 10 having a shape for covering front and side faces of jack body 2. Shield plate 3 also has a pressing piece 11 arranged continuously with, and below, covering portion 10. Shield plate 3 is formed from a single conductive metallic plate.
Pressing piece 11 is arm shaped, which permits the capability of a leafspring type response. Pressing piece 11 is integral with, and slanting forward from, a front face of covering portion 10. When sleeve portion 8 of jack body 2 is inserted into metallic chassis 9, pressing piece 11 is pressed against the front face of jack body 2 and resiliently contacts metallic chassis 9. A sleeve contact piece 12 projects vertically downward and is integral with pressing piece 11.
Shield plate 3 is mounted to jack body 2 with sleeve portion 8 inserted into a through hole 10a on the front face of covering portion 10. Sleeve contact piece 12 extends along leg portion 5a of the sleeve terminal and is solder-connected to a ground pattern on a portion of circuit board 4. Leg portion 5a of the sleeve terminal is also solder-connected to the ground pattern so that sleeve contact piece 12 and leg portion 5a are connected to ground.
Accordingly, metallic chassis 9, shield plate 3 and the sleeve terminal are electrically connected to the ground pattern and have a ground electric potential. Furthermore, the front face and both the side faces of jack body 2 are covered by shield plate 3. The terminals within jack body 2 are shielded from external interference from electrical noise, while reducing noise radiation from the device.
With this conventional structure, the jack is shielded from interfering noise on the front face and the left-hand and right-hand side faces of the jack body 2, but is not shielded on a surface facing circuit board 4. Accordingly, a high frequency signal is transmitted through the insulating housing of the jack and circuit board 4. Jack body 2 is thus exposed to high frequency noise entering through the terminals on jack body 2, which causes a mutual interference with other circuit parts mounted on circuit board 4.
Conventional means for limiting the effects of interfering noise involve temporarily mounting jack body 2 on circuit board 4 and injecting high frequency noise through the terminals connected to jack body 2 from a noise generating source. The noise received by other noise-susceptible devices on circuit board 4 is then measured. Based on the measurements, techniques for reducing the effect of noise on the circuit configuration are taken, such as a recombination of circuits, etc. These steps taken to reduce the impact of noise contribute to increasing the complexity and length of time involved in completing production of a device.